Compositions having a low gas permeation performance (gas barrier performance) composed of thermoplastic resin/thermoplastic resin-based blends such as a high density polyethylene resin and nylon 6 or nylon 66 (HDPE/PA6.66), a polyethylene terephthalate and aromatic nylon (PET/MXD6), a polyethylene terephthalate and vinyl alcohol-ethylene copolymer (PET/EVOH), where one thermoplastic resin is layered over the other layer to form plural layers by molding, and processes for producing the same, are already known from Isao Hata: Kobunshi (Polymers), 40 (4), p. 244 (1991) etc. Further, an application regarding the use of such a composition as the inner layer of a tire has been already filed by the present assignee (Japanese Patent Application No. 7-55929). However, since these materials are thermoplastic resin/thermoplastic resin blends, while they are superior in gas barrier property, they lack flexibility, and therefore, such films are liable to break when the tire is in running.
Further, there are also examples of use of a thermoplastic elastomer composed of a rubber and a thermoplastic resin for the inner liner or a tire (Japanese Patent Application No. 8-183683), but in general a flexible material superior in durability has a low heat resistance. With a thermoplastic elastomer using a thermoplastic resin having a melting point less-than the tire vulcanization temperature as a matrix, when the vulcanization bladder is released at the end of the vulcanization of the tire, the tire inside surface is liable to become poor in appearance due to the thermoplastic resin sticking to the bladder, rubbing with the bladder, etc.
Research directed to the difference in viscosities at the time of processing in mixing of rubbers and resins has been known in the past. Among these, the capability of reducing the domain dispersion particle size the most in the state where the ratio of melt viscosities of the rubber/resin is brought close to 1 (that is, no difference in viscosities) has been reported in S. Wu, Polym. Eng. Sci., 27(5), 1987. If using these technologies to fabricate a thermoplastic elastomer having more flexibility, larger strength and elongation, and superior durability by raising the rubber ratio, while keeping the ratio of melt viscosities of the rubber/resin at 1, the rubber becomes the matrix and thermoplasticity is no longer exhibited.
In a laminate in which dynamic fatigue resistance is required such as tire, hose, when using a gas permeation preventive thermoplastic elastomer composition composed of rubber/resin dispersed therein, it is known to obtain a balance between the flexibility and gas permeation preventive property by making joint use of a flexible N11- or N12-nylon and superior gas permeation preventive property N6- or N66-nylon. Further, the present inventors have proposed to define the volume fraction and melt viscosity using the equation of α:(φd/φm)×(ηm/ηd)<1.0wherein the volume fractions of the continuous phase component and dispersion phase component in the thermoplastic elastomer composition are φm and φd and the melt viscosities of the components are ηm and ηd and further to bring the ratio of viscosities ηm/ηd close to 1 to reduce the rubber dispersed particle size of the domain to improve the durability (Japanese Patent Application No. 8-193545, Japanese Patent Application No. 9-175150, and Japanese Patent Application No. 10-235386). However, the durability at low temperatures was insufficient by just reducing the rubber particle size.